Method of shaping thermoplastic sheets



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ATTORNEYS United States Patent 3,419,651 METHOD OF SHAPING THERMOPLASTIC SHEETS Alfred H. Miller, Glenn Perry, and Lawrence C. Wheat, Toledo, Ohio, assignors to Libbey-Oweus-Ford Glass Company, Toledo, Ohio, a corporation of Ohio Original application Oct. 21, 1964, Ser. No. 405,383, now Patent No. 3,341,889, dated Sept. 19, 1967. Divided and this application July 18, 1967, Ser. No. 672,661

8 Claims. (Cl. 264160) ABSTRACT OF THE DISCLOSURE Method of shaping thermoplastic sheets for use as interlayers in laminated safety glass. A substantially continuous sheet of plastic is drawn from a source of supply over a substantially horizontal supporting surface and the free end thereof clamped in a fixed position. Lengthwise tension is then applied to the continuous sheet by exerting a rearward pull thereon from the clamped free end thereof, after which the sheet is clamped at a point inwardly of the clamped free end and while maintained in tension, is cut to provide an individual sheet clamped at its opposite ends. The sheet is then supported vertically and conveyed first through a heating zone in which it is softened and shaped by sagging of the sheet in the plane of the sheet and then through a cooling zone in which the sheet is set in its shaped condition.

This application is a division of application Ser No. 405,383, filed Oct. 21, 1964.

The present invention relates generally to the manufacture of glare-reducing windows, or the like and more particularly to an improved method for shaping the plastic interlayer for curved or bent laminated safety glass windshields or windows when said interlayer is provided with a glare-reducing portion.

In shaping the plastic interlayers for laminated safety glass Windshields or windows it has been customary to first cut a continuous length or roll of plastic into individual sheets, and then clamp each individual sheet along two opposite edges only in a frame to hold it in its normal shape Tractive forces are then applied to the lower unsupported edge of the sheet while supporting the frame and sheet in a vertical position and simultaneously heating the sheet until it has been stretched or shaped in the desired manner. After heating, the sheet is cooled to retain its desired shape. It has heretofore been the practice to clamp only a single sheet of plastic in a frame, with a plurality of such frames being hung in a vertical position on a rack or truck which is then passed first into a heating chamber and subsequently into a cooling chamber.

While the invention is applicable to the shaping of individual plastic sheets supported in separate frames, it is of particular utility where a plurality of continuous lengths of thermoplastic material are withdrawn from separate sources of supply and, while superimposed one upon the other, are clamped at their free ends in a frame and uniformly stretched or placed in tension. While maintained in tension, the continuous lengths of plastic are also clamped in the frame at a point remote from the free ends thereof and then cut transversely from the continuous lengths outwardly of the frame to provide a plurality of individual sheets. A succession of frames,

each with a plurality of uniformly taut or tensioned sheets clamped therein, are supported in vertical position and moved in spaced relation first through a. heating zone and then through a cooling zone. During the heating of the sheets, tractive forces applied to the lower unsupported edges thereof cause said sheets to be stretched or distorted in the plane of the sheets to the desired curvature or shape.

As herein provided, the air in both the heating zone and cooling zone is maintained within desired ranges of working temperatures whereby the plastic sheets will become shaped while heat-softened and then set in the desired curvature to which they were shaped as they are cooled. To obtain gradual drying of the sheets as they cool, conditioned air is supplied to the coooling zone and as the frames reach the exit end of said cooling zone, they are successively conveyed with the shaped sheets into a room of closely controlled temperature and humidity to obviate the tendency of the plastic to relax, due to its elastic memory, from the curvature to which it was shaped. The plastic sheets are maintained under such controlled conditions until assembled with the glass sheets in the manufacture of laminated safety glass.

It is, therefore, a primary object of the present invention to provide an improved method of shaping sheets of plastic material employed as the interlayer in the production of curved or bent laminated safety glass windows or Windshields having a glare-reducing area in a substantially continuous manner.

Another object of the invention is to provide a method of shaping plastic sheets having a colored band along and parallel to one marginal edge of the sheet, in which a substantially continuous length of plastic material is withdrawn from a source of supply and clamped at the free end thereof in one end of a frame and also clamped at a point remote from said free end in the opposite end of said frame, the plastic being then cut transversely outwardly of the frame to form an individual sheet of predetermined size, the frame with the sheet clamped therein being hung in a vertical position with the colored band at the upper edge thereof, and tractive forces being applied to the lower edge of the sheet and in the plane of the sheet and the sheet then heated to cause it to be deflected downwardly resulting in the upper and lower longitudinal edges thereof being curved in the same direction, after which the sheet is cooled.

Another object of the invention is to provide such a method wherein a plurality of substantially continuous lengths of plastic material are drawn from a plurality of sources of supply and sections of predetermined length transversely clamped in a frame along two spaced lines in such a manner as to place the clamped sections under uniform tension, after which the continuous lengths of plastic are cut transversely outwardly of the frame to provide individual sheets which are shaped in the above manner.

Another object of the invention is to provide such a method in which the substantially continuous lengths of plastic material are drawn from the sources of supply in superimposed contacting relation between a pair of feed rolls and the free ends thereof clamped together, after which the feed rolls are moved outwardly to place the plastic material under tension, the plastic material being then clamped inwardly of the free ends thereof to provide uniformly taut sections of predetermined length before the continuous lengths of plastic are cut to form individual sheets.

A further object of the invention is to provide such a method in which the plurality of substantially continuous lengths of plastic material after being drawn from their separate sources of supply and before passing between the feed rolls are permitted, while hanging in freely suspended loops, to relax and obtain a uniformity of lineal tension prior to their being clamped in a frame and cut into individual sheets.

A further object of the invention is to provide such a method in which a plurality of frames, each having a plurality of plastic sheets clamped therein, are hung in a vertical position and moved substantially continuously in spaced relation to one another through a zone of controlled humidity and heated air to cause the plurality of sheets to be shaped by downward deflection and then passed through a zone of controlled humidity and cooling air to set the shaped curvature therein after which the sheets are removed from each of the frames for storage in a room having controlled temperature and humidity.

Other objects and advantages of the invention will become more apparent during the course of the following description when read in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate like parts throughout the same:

FIG. 1 is a perspective view of a windshield, produced in accordance with this invention, shown in its functional position in the windshield opening of an automobile;

FIG. 2 is a front elevation of the windshield;

FIG. 3 is a transverse vertical sectional view taken on the line 33 of FIG. 2;

FIG. 4 is a front elevation of a support frame for distortion of thermoplastic sheets in accordance with the invention;

FIG. 5 is an end elevation of the support frame;

FIG. 6 is a longitudinal vertical section taken on line 66 of FIG. 5;

FIG. 7 is a transverse vertical section taken on line 7-7 of FIG. 4;

FIG. 8 is a horizontal section taken on line 88 of FIG. 4;

FIG. 9 is an enlarged detail view of a clamping member of the support frame;

FIG. 10 is a schematic side elevation of a contiuuuous distortion apparatus constructed in accordance with the invention;

FIG. 11 is an enlarged longitudinal vertical section of one end of the apparatus;

FIG. 12 is a transverse vertical section taken on line 1212 of FIG. 10;

FIG. 13 is a horizontal section taken on line 1313 of FIG. 11;

FIG. 14 is a horizontal section of a roll stand and taken on line 1414 of FIG. 12;

FIG. 15 is a fragmentary view of the upper end of a thermoplastic sheeting feeder unit;

FIG. 16 is a horizontal section taken on line 1616 of FIG. 15;

FIG. 17 is a transverse vertical section taken on line 1717 of FIG. 15, and illustrates the upper end of the feeder unit;

FIG. 18 is a detail view at the lower end of the feeder unit;

FIG. 19 is a fragmentary perspective view of one form of conveyor chain and of a support track on which the same is supported;

FIG. 20 is a plan view of an assembly and stretching unit;

FIG. 21 is an enlarged fragmentary side elevation of the assembly unit;

FIG. 22 is a view of one end of the assembly unit;

FIG. 23 is a similar view of the opposite end of the unit;

FIG. 24 is a longitudinal vertical section of the unit and as taken on line 2424 of FIG. 22;

FIG. 25 is a longitudinal section taken on line 25-25 of FIG. 23;

FIG. 26 is a horizontal section taken on line 26-26 of FIG. 22;

FIG. 27 is a transverse vertical section taken on line 27-27 of FIG. 24;

FIG. 28 is a transverse vertical section taken on line 2828 of FIG. 25;

FIG. 29 is a transverse vertical section taken on line 29-29 of FIG. 22;

FIG. 30 is an enlarged detail view taken on line 3030 of FIG. 20;

FIG. 31 is an enlarged detail view taken on line 31-31 of FIG. 20;

FIG. 32 is a fragmentary elevation of a tension control device;

FIG. 33 is a perspective view of the frame structure of the assembly and stretching unit;

FIG. 34 is a perspective view of a clamp and traction element;

FIG. 35 is a longitudinal vertical section of the entry end of the heating oven;

FIG. 36 is a fragmentary plan view illustrating latching means for locating the frames in spaced order within the heating oven;

FIG. 37 is a side elevation of the latching means;

FIG. 38 is a plan view of the latching means;

FIG. 39 is a transverse vertical section of one transfer area of the apparatus as taken on line 3939 of FIG. 10;

FIG. 40 is a longitudinal vertical section taken on line 4040 of FIG. 39;

FIG. 41 is a horizontal section taken on line 4141 of FIG. 39;

FIG. 42 is a horizontal section taken on line 42-42 of FIG. 39;

FIG. 43 is a fragmentary detail view;

FIG. 44 is a perspective view of a conveyor chain support member;

FIG. 45 is a detail view of a part of the conveyor systems;

FIG. 46 is an end elevation of a second transfer area of the apparatus;

FIG. 47 is a longitudinal vertical section taken on line 4747 of FIG. 46;

FIG. 48 is a horizontal section taken on line 4848 of FIG. 47;

FIG. 49 is a transverse vertical section taken on line 4949 of FIG. 48;

FIG. 50 is an enlarged horizontal section taken on line 50-50 of FIG. 47;

FIGS. 51-56 are a series of views illustrating the sequential steps carried out in the assembly of thermoplastic sheets on a support frame; and

FIG. 57 is a front elevation of a windshield embodying a modified form of the invention.

In FIG. 1 of the drawings, there is shown a windshield 10 as it appears from the outside of the automobile 11 in which the windshield is mounted. The windshield 10 is of a conventional laminated glass construction in that it comprises (FIG. 3) two sheets of glass 12 and 13 and a non-brittle plastic interlayer 14 such as polyvinyl *butyra1 resin, interposed therebetween. The windshield 10 of FIG. 1, or as shown in plan in FIG. 2 includes a glarereducing area 15 which is a neutral shading within the windshield itself and is vignetted or graduated in shade from a deep or dark hue as at 16, along the upper margin of the windshield, which may be opaque, or nearly opaque, to a very light hue as at 17, in the area adjacent the essentially transparent viewing area 18 through which the driver clearly see sthe road and approaching traffic. The utility and advantages of the glare-reducing area or band are of course immediately apparent and presently well- 

